1. Field of the Invention
The present invention relates to a transmitting apparatus and method, and more specifically, it relates to a transmitting apparatus and method that allow communication with less noise.
2. Description of Related Art
In recent years, a so-called passive entry system that performs hands-free locking and unlocking automatically, for example, has been in practical use as an entry system for vehicles, and the wider spread in the future is being expected (refer to JP-A-2003-269023 (Patent Document 1), for example). This automatically implements operations (unlocking/locking operations) by a locking mechanism for a vehicle door by controlling a vehicle-mounted machine by performing bidirectional wireless communication between a portable machine, which can be carried by a user, and the vehicle-mounted machine to check the authenticity of the portable machine and analyze the position of the portable machine, for example, based on electromagnetic waves (signal) received from the portable machine by the vehicle-mounted machine.
The future wide spread of a TPMS (tire pressure monitoring system) that detects the air pressure of a tire and alarming a user if any abnormality exists is also expected. This performs bidirectional wireless communication between a sensor that senses the air pressure of a tire and a vehicle-mounted machine, determines an abnormality in air pressure, for example, based on electromagnetic waves (signal) received from a sensor by a vehicle-mounted machine and outputs an alarm with an indicator or by voice as required.
In a passive entry system or a TPMS, an antenna connecting to a vehicle-mounted machine is placed at a predetermined position in a vehicle, and communication is performed between the vehicle-mounted machine and the portable machine or sensor by transmitting a signal of LF (Low Frequency) waves (at 100 to 200 KHz, for example) to the portable machine or a sensor as required and receiving the signal transmitted from the portable machine or sensor by the antenna.
In a passive entry system or a TPMS, a distance to some extent exists between the position where an antenna is placed and the position where an ECU (Electronic Control Unit) is placed that generates signals and performs various kinds of control. For that reason, when a driving circuit that drives an antenna is provided in the ECU (Electronic Control Unit), the driving circuit and the antenna are connected through two harnesses. A large amount of current for driving the antenna flows through the harnesses. This causes unnecessary radiation noise, which may cause noise in radio and/or may have an adverse effect to operations by other electronic machines installed in the vehicle. In other words, the integral configuration of the driving circuit that drives the antenna and the ECU is not desirable, and the driving circuit is generally integrated with the antenna.
For that reason, the ECU and the driving circuit must be connected through three harnesses of a power supply line, a ground line and a signal line, which means an increase in number of harnesses. However, the increase in number of harnesses has an influence on the structure and/or production costs of vehicles.